Plantronics T20

The Plantronics T20 is a complete, dual-line telephone with an ergonomically designed, convertible headset. Includes all the features of the T10 single-line headset telephone, plus a handy call hold button and three-way conference calling.
T20 Options
Plantronics T20 (45162-11)
Dual-line telephone with headset, features include line selection and hold and three-way conferencing.